There is a rotary attachment mechanism disclosed in Patent Document 1 as one example of a conventional hinge mechanism having a clicking action. The rotary attachment mechanism has a shaft that passes through a base, a clicking spring, and a clicking plate, and the clicking plate is secured to the shaft. The clicking spring is a plate spring having resiliency in a direction parallel to the central axis of the shaft, and a protrusion for a clicking function to be fit into a recess of the clicking plate is formed in the position corresponding to the curved top of the clicking plate. In addition, vertically bent ends are provided on the clicking spring, and the ends are engaged with engaging holes formed in the base, so that the base and the clicking spring are fixed in an arrangement to be fit into the holes with a slight play. When the shaft rotates, the clicking plate rotates with the shaft, and the protrusion of the clicking spring fits in or comes out of the recess of the clicking plate, thereby generating a clicking action.
When the shaft rotates, the clicking spring is pushed in the rotating direction by the dimension of play, and further twisted in the rotating direction by the friction between the clicking spring and clicking plate, with the result that the ends of the clicking spring lift up from the base. Therefore, there is a problem such that the moment when the protrusion of the clicking spring is fitted into the recess in the clicking plate, the clicking spring and the clicking plate collide against each other by the released spring force of the clicking spring, whereby a very large sound of the collision (clicking sound) is generated.
On the other hand, caulking is commonly used for fastening a plate spring with a shaft to generate a rotation torque as is employed in a conventional hinge mechanism. However, caulking directly the shaft to the plate spring may cause a stress to be concentrated at the caulked portion when the plate spring is deflected, which may loosen the caulking. Moreover, a high load cannot be obtained since there is no holding member on the side toward which the spring is deflected. Therefore, conventionally, a fastening plate is laminated on the side toward which the spring is deflected, and then the fastening plate and the shaft are arranged by caulking; thus, a stress where the plate spring is deflected is dispersed to the fastening plate to prevent loosening of the caulked portion, and also the plate spring can be deflected outside the fastening plate to thus obtain a high load.